1. Field of the Invention
The present invention relates to a capacitance type sensor suitable for detecting a force externally applied.
2. Description of Related Art
A capacitance type sensor is generally used for converting into electrical signals the magnitude and direction of a force applied by an operator. For example, in an input device for a computer, a capacitance type sensor for inputting multidimensional operations is incorporated as a so-called joystick.
In the capacitance type sensor, an operation quantity having a predetermined dynamic range can be input as the magnitude of a force applied by the operator. In addition, such a capacitance type sensor is used also as a two- or three-dimensional sensor capable of resolving into each dimensional component an applied force to be detected. In particular, capacitance type sensors in which a capacitance element is formed between two electrodes to detect a force on the basis of a change in capacitance value caused by a change in the distance between the electrodes, have been put into practical use in various fields because they have a merit that the construction can be simplified to intend to reduce the cost.
For example, JP-A-2001-91382 discloses a capacitance type sensor in which fixed electrodes on the X-axis, fixed electrodes on the Y-axis, and a fixed electrode on the Z-axis surrounded by the X- and Y-axial fixed electrodes, cooperate with a movable electrode plate to form variable capacitance elements. In the capacitance type sensor, for example, when an X-axial force Fx is applied to an operation portion, the distance between a fixed electrode on the X-axis and the movable electrode plate is decreased to increase the capacitance value of the capacitance element formed by the electrodes. Therefore, by detecting the change in capacitance value of the capacitance element, an X-axial signal corresponding to the X-axial force Fx can be output.
In the capacitance type sensor, however, an X-axial signal corresponding to an X-axial force Fx, a Y-axial signal corresponding to a Y-axial force Fy, and a Z-axial signal corresponding to a Z-axial force Fz, are always output when any force is applied to the operation portion. Therefore, when only the X- or Y-axial output is intended to be changed, the Z-axial output may also change. On the other hand, when only the Z-axial output is intended to be changed, the X- or Y-axial output may also change.
For example, in the case that the capacitance type sensor is applied to a joystick for moving a cursor on the basis of X- and Y-axial outputs, and performing a predetermined operation such as clicking on the basis of a Z-axial output, the cursor is moved to a predetermined position, for example, on an icon, by changing the X- and Y-axial outputs, and then the predetermined operation is performed by changing the Z-axial output. In this case, however, when a force is applied for moving the cursor, the predetermined operation may be erroneously performed because not only the X- and Y-axial outputs but also the Z-axial output changes. On the other hand, when a force is applied for performing the predetermined operation, the cursor may be moved because not only the Z-axial output but also the X- and Y-axial outputs change. This makes it difficult to perform the predetermined operation with keeping the cursor at the predetermined position.